%用于计算只考虑一阶项力时的本征模和本征频率（以omega0 = sqrt(K/M)为单位）
function [evector, omega] = eigen_cal(N)
    
    %构建矩阵
    offdiag = -ones(1,N-1);
    ondiag = 2 * ones(1,N);
    A = diag(ondiag) + diag(offdiag,1) + diag(offdiag,-1);
    
    [evector, evalue] = eig(A);
    
    omega = sqrt(evalue);
    
    return

end